Electrostatic Dispersion of Drops in Clusters

Abstract

A theory of evaporation and dispersion of electrostatically charged drops has been developed for drops belonging to a spherical cluster exposed to a flow Under the assumption of constant atmospheric pressure, the quasi-steady approximation was made for the gas phase whereas the drop-temperature history is unsteady. The model lakes into account interdrop interactions (in terms of heal and mass transfer) due to drop proximity, turbulence exchange processes between the cluster and its surroundings and electrostatic force effects due to the charge on the drops. Calculations based upon this model were made for charged as well as uncharged clusters of drops. The charge was varied from a null value to the maximum possible charge found empirically for hydrocarbon sprays. Moreover, the turbulence model was varied in such a way as to simulate the cluster embedded into a flow where turbulence develops with time (Model 1) or a flow with pre-existing turbulence (Model 2). The results show that the control parameters for the evaporation of charged drops are different from those for uncharged drops in dense clusters; turbulence levels which were shown lo be crucial for the latter in the dense cluster regime do not affect the former in the same regime. For dilute clusters turbulence is unimportant in both cases. Moreover, drop charging docs not affect dilute clusters of drops whereas dense clusters of drops are substantially affected. Based upon existing experimental data, inferences are made about how electrostatic spray dispersion can affect soot control in powersystems using fuel sprays. Limited results perlainingto the ignition of nearly-dense clusters of electrostatically charged drops are discussed as well.

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